1. Field of the Invention
The present invention relates to a complex relay device that has multiple assembled relays.
2. Description of Related Art
JP-A-2002-343216 describes a complex relay device. This complex relay device uses a bus bar base plate, on which multiple bus bars are formed in a predetermined circuit pattern. The bus bars except for at least a relay connection terminal and an external connection terminal of the bus bars are covered with a resin. The multiple bus bars are integrated so that the external connection terminal is connected with the relay connection terminal through the bus bars. Multiple relay units are fixed and connected to the bus bar base plate. The complex relay device communizes a circuit base plate or external terminals for a plurality of relay units. Therefore, wiring work can be simplified and the multiplicity of relays can be located in a compact space.
Usually, the relay units or wiring of the complex relay device are accommodated in a resin relay case to improve waterproof property, dustproof property, and strength.
It is difficult to use the complex relay device in an environment in which a thermal condition or a vibration condition is harsh, e.g., in an engine compartment for the following reasons.
Since high rigidity is required in such a harsh environment, thickness of the relay case should be increased. As a result, the temperature inside a relay accommodation space formed in the relay case increases. Specifically, out of the multiplicity of relay units arranged in line on a side surface of the bus bar base plate, the relay unit at a central portion of the relay case suffers a more severe temperature increase than the relay units at peripheral portions of the relay case. This occurs because the relay unit at the central portion receives heat from both adjacent relay units and has a small heat radiation area facing the relay case.
As a result, electric resistance of a contact circuit in the relay unit, which is formed by a spring and the bus bar wiring between a contact of the relay unit and the external terminal, becomes larger in the relay unit at the central portion than in the relay units at peripheral portions. Accordingly, resistance loss and heat generation increase and a maximum contact current value for opening or closing the contact decreases in the relay unit at the central portion. If a multiplicity of relay units are arranged in the vibration-resistant, thick and hermetic case, the temperature of the relay unit at the central portion increases compared to that of the relay units at the peripheral portions. Accordingly, the current capable of flowing through the relay units is reduced. The increase in the resistance of the contact circuit of the relay unit at the central portion causes a further increase the generation of heat.
The temperature increase at the relay unit at the central portion greater than the temperature increase at the relay units at the peripheral portions will increase coil resistance of the relay unit at the central portion and deteriorate magnetic characteristics of the relay unit at the central portion. In order for the relay unit at the central portion to operate properly, coil current flowing through the coil of the relay unit at the central portion has to be increased compared to coil current flowing through the coils of the relay units at the peripheral portions. Therefore, voltage (coil application voltage) applied to the relay unit has to be increased compared to that of a single relay. As a result, the temperature increase in the relay case, specifically, the temperature increase at the central portion of the relay case, will enlarge.
If the complex relay device, which integrates multiple relays, is used in a high-temperature and high-vibration environment, the relay device is increased in its size and weight compared to the case where single relays are used, because reduction of the contact circuit resistance and coil resistance is necessary. Accordingly, using the necessary number of single-relay devices is more advantageous than using the complex relay device with respect to compactness.